In a typical die stamping apparatus, it is desired to accurately cut, punch or form a part. Such apparatus usually comprises an upper die and a lower die movable with respect to the lower die. In the forming of parts, it has been common to provide a delay in the movement of the lower die upwardly after the part has been formed, cut or punched from the workpiece. Such a time delay has been produced by cam control of the lower die or by a hydraulic system associated with the lower die. A typical example of a hydraulic system is shown in U.S. Pat. Nos. 2,694,567 and 3,570,343.
Such hydraulic systems have a disadvantage in that they require associated hydraulic fluid lines, valves and the like externally of the hydraulic cushion on the press.
In co-pending application Ser. No. 099,914, filed Sept. 22, 1987 now U.S. Pat. No. 4,774,865 having a common assignee with the present application, there is disclosed an arrangement wherein each cylinder assembly includes a first piston associated with and exposed to the inert gas such as nitrogen in the manifold and a second piston engaged by the first piston and urged outwardly into engagement with a punch base. A hydraulic circuit is associated with the second piston and controlled by a valve such that upon downward movement of the first piston hydraulic fluid may flow freely without inhibiting the movement of the first piston, but upon actuation of the valve hydraulic fluid locks the first piston and thereby prevents it from moving upwardly until the valve is actuated so that a predetermined time delay is provided.
Among the objectives of the present invention are to provide a die stamping system which can be provided within the confines of conventional apparatus; which will provide the desired time delay; wherein the time delay can be readily adjusted as desired without disassembling the system; wherein the delay action is positive; which eliminates the need for hydraulic hoses between adjacent cylinder assemblies; wherein heat cylinder assembly can be readily mounted on a manifold without the need for circumferential orientation; wherein the cylinder assemblies have a low profile; wherein the cylinder assemblies can be readily filled with hydraulic fluids; wherein the cylinder assemblies have effective seals; and wherein cylinder assemblies have provision for pressure relief to avoid damage thereto.
In accordance with the invention, each cylinder assembly includes a piston associated with and exposed to the nitrogen in the manifold and to hydraulic pressure. The cylinder assemblies are connected to a single hydraulic valve which has associated therewith an accumulator and which is operated simultaneously to actuate the cylinders. The hydraulic lines to the cylinders are provided in the manifold.